Knowing when to stop filling a tank with liquid before the tank overflows is desirable, especially when the liquid is pollutant, toxic, corrosive, flammable, or expensive; however, knowing when to stop filling the tank is not always easy when the contents of the tank are not visible to a person filling the tank.
Various systems and methods have been developed to deal with this problem. For example, some filling devices, such as gasoline pumps that are commonly available at urban filling stations for filling the tanks of automobiles and other urban vehicles, sense when a vehicle's fuel tank becomes full and automatically stop fueling.
While such gasoline pumps are commonly available for filling the tanks of automobiles and other vehicles in urban areas, they are not as widely available for use in filling the tanks of other types of vehicles and machinery, including jet propulsion watercraft and other small boats, snowmobiles and other recreational vehicles, and tractors and other farming or rural machinery. These types of vehicles and machines are frequently filled using smaller, less sophisticated filling devices that are not equipped to automatically stop fueling when they sense that the tank they are filling is full. Thus, tanks may overflow, and, in the case of small watercraft being filled with fuel while sitting in water, the spilled fuel often falls into the water.
One current attempt to address the overflow problem, especially in connection with watercraft, snowmobiles, and other recreational vehicles, has been the installation of alarm devices within a fuel tank that sense a fuel level in the tank and that sound an alarm when the tank approaches an overflow state. Unfortunately, such solutions rely on one or more devices that constantly draw a small amount of electrical current from the craft's electrical system. Since recreational vehicles often spend long periods of time unused, even this small draw of electricity can eventually deplete the craft's entire electrical supply and leave the battery dead.
Attempts to alleviate this problem by providing a mechanism which allows a person to manually turn off the alarm device suffer from the disadvantages that the person must first remember to turn the alarm device off if the electrical supply is to be protected against depletion and, second, must remember to turn the alarm device back on again if the tank is to be protected against overflow. Frequently, people forget to diligently carry out these two steps, and the system does not work as desired.